Animal Waste, Water Quality and Human Health

122Animal Waste, Water Quality and Human HealthMolecular fingerprinting of pathogens such as C. jejuni has allowed a morethorough examination of the movement of these important pathogens into andout of poultry barns and highlighted the importance of maintaining biosecurity(Bull et al. 2006). For example, these studies have underlined the importance ofhuman and insect vectors and even wind in the transmission of these pathogensamong flocks.In animals such as cattle, sheep and goats, that are raised on pasture, and infeedlots and in free-range poultry flocks or swine herds, biosecurity is asignificantly greater challenge. Transmission of waterborne pathogens suchas G. duodenalis, Crypto. parvum, Campylobacter, Salmonella, E. coliO157:H7, and Leptospira interrogans among cattle in herds and between cattleand wildlife species is known to occur and is difficult to prevent in openpastures (Keene et al. 1997, Lomar et al. 2000, Thompson 2000, Daniels et al.2003, Liebana et al. 2003, Wahlstrom et al. 2003). In cattle herds it isrecommended to limit the introduction of new animals, to move dams andtheir calves away from birthing areas onto clean pastures after parturition, and toisolate dairy calves from other calves and the rest of the herd. This isparticularly important for agents such as Crypto. parvum whose populationsappear to be largely maintained by calf-to-calf transmission. It has alsobeen demonstrated that reducing animal stocking densities reducesthe exposure of susceptible animals to infected animals and their excreta. Forexample, reducing the stocking density in a high-cattle-use area was shown tobe associated with a reduction in G. duodenalis cysts in rainfall-associatedrunoff.Biosecurity is easy to recommend but can be hard to implement. The recentavian influenza pandemic in Southeast Asia has shown how difficult it is tomaintain biosecurity in intensive production systems, while in smallholdersystems in developing countries high levels of biosecurity are probablyunattainable. Good hygienic practices may reduce the pressure of infection butconverting the existing low input systems into biosecure systems might renderthem uneconomic and unworkable.A more fundamental challenge in advocating of biosecurity messages is that,until recently, most recommended procedures have been based on commonsenserather than scientific evidence. Unfortunately, the most important sources ofmany zoonotic enteric pathogens in flocks and herds have not been quantifiedand are only starting to be investigated. Case-control and other risk-factorstudies are needed to develop evidence-based biosecurity recommendations,where most emphasis is placed on steps shown to be critical in reducing thepathogen prevalence rate in animal populations. These are discussed in moredetail later in this Chapter.